Combined internal combustion and hot-air engine



DLAHUH ROOM-- 0-280. OR 3.180.078 SR ,April 27, 1965 J. LlsToN 3.180,078

COMBINED INTERNAL COMBUSTION AND HOT AIR ENGINE Filed April 14, 1961'lasera /s ro/v,

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,April 27, 1965 J. Lls'roN 3,180073 COMBINED INTERNAL COMBUSTION ANDHOT-AIR ENGINE Filed April 14. 1981 5 Sheets-Sheet 2 A rromvef's.

April 27, 1965 J. LlsToN 3,180,078

COMBINED INTERNAL COMBUSTION AND HOT-AIR ENGINE Filed April 14. 1961 3Sheets-Sheet S Arroemsrs.

United States Patent O 3.180,078 COMBINED INTERNAL COMBUSTION ANDHOT-AIR ENGINE Joseph Liston, Lafayette, Ind. (900 Robinson St., WestLafayette, Ind.) Filed Apr. 14, 1961, Ser. No. 103,044 4 Claims. (Cl.60-14) The subject matter of this invention is a two-stage power plantor prime mover, the first stage of which is an internal combustionengine and the second stage of which is a hot-air or Stirling-cycleengine operated by heat derived from the gases exhausted by the firststage. An arrangement heretofore proposed for utilizing in a Stirlingengine heat contained in the exhaust gases from an internal combustionengine employed a cylinder and piston combination in which the head-endof the cylinder functioned as a combustion space, as in an ordinaryinternal combustion engine, and the crank-end of the cylinder functionedas the cold space of a Stirling engine. In that arrangement, inwardmovement of the piston under pressure generated by combustion compressedthe gaseous working medium of the Stirling engine and displaced it intoa heat-exchanger where it absorbed heat from the gases exhausted fromthe head-end of the cylinder. After bottom dead-center, the compressedand heated working medium expanded into the crank-end of the cylinderimpelling the piston outwardly. Such an arrangement has severaldisadvantages. In the first place, there is an inevitable andundesirable transfer of heat from the combustion space to theStirling-engine cold space by conduction through the piston and cylinderwall. In the second place, it is desirable that the fixed quantity ofworking medium employed in the Stirlng engine be maintained undersubstantial pressure, and the low fluid pressures which would exist inthe combustion space just before compression and during the initialstages thereof would contribute to the escape of the working medium pastthe piston. Again, since a single piston is used, Variation in thedisplacements of the two engines could be obtained only by employing apiston and cylinder each having portions of different diameter, whichwould result in complicating the construction, increasing cost, andincreasing the weight of the piston. Still further, a reasonably uniformdistribution of torque impulses would be obtained only if the head-endof the cylinder operated on a two-stroke cycle, for a Stirling enginedelivers a torque impulse for each revolution of the crankshaft.

It is an object of this invention to produce a prime mover having aninternal-combustion engine as a first stage and a Stirling engine as asecond stage and to utilize in the Stirling engine the heat contained inor derivable from the exhaust gases of the internal-combustion engine.Another object of the invention is to make available for use in theStirling engine heat derived from the combustion of unburned fuelcontained in the exhaust from the internal-combustion engine.

According to one feature of the present invention, the pistons andcylinders of the two stages are independent of each other, although thepistons are preferably operatively interconnected, most desirably bybeing associated with a common crankshaft. Operatively interconnectingthe pistons of the two stages makes possible a predetermineddistribution of torque impulses; and by properly arranging the cylindersof the two engines, the distribution of torque impulses can be madesubstantially uniform.

In accordance with another feature of my invention, I provide, in theconduit through which exhaust gases from the first stage flow to thesecond stage, means for burning any fuel unburned in the first stage.

Other objects and features of my invention will become 3,l80,078Patented Apr. 27, 1965 ICC apparent from the following more detaileddescription and from the accompanying drawings in which:

FIG. l is an isometric view, largely diagrammatic in Character, of atwo-stage power plant wherein the Stirling engine is a two-cylinder,V-type engine disposed in the re` gion between the cylinders of atwo-cylinder, in-line internal combustion engine of the four-strokecycle type;

FIG. 2 is a section through the two cylinders of the Stirling engineincorporated in the power plant of FIG. l;

FIG. 3 is a longitudinal section through the same power plant in theplane of the cylinders of the internalcombustion engine;

FIG. 4 is a diagrammatic view illustrating means for burning fuelunburned in the internal-combustion engine;

FIG. 5 is an isometric view somewhat diagrammatic in Character, of apower plant embodying the invention and employing a single-cylinder,two-stroke cycle internal combustion engine as a first stage; and

FIG. 6 is a diagrammatic view illustrating the form of a crankshaft forthe power plant of FIG. 5.

The engine shown in FIGS. 1-3 comprises a crankcase 10 within which acrankshaft 11 is rotatably supported. Two cylinders 12 and 13 of aninternal combustion engine are mounted on the crankcase near the endsthereof and in a common plane. Between the two cylinders 12 and 13, thecrankcase supports two cylinders 15 and 16 of a Stirling engine, suchtwo cylinders being disposed at an angle to each other and symmetricallywith respect to the common plane of the cylinders 12 and 13. Thecylinders 12 and 13 contain pistons 18 connected by connecting rods 19to cranks 20 of the crankshaft 11, such cranks being coaxial with eachother. The cylinders 15 and 16 contain pistons 22 connected byconnecting rods 23 with a common crank 24 coplanar with butdiametrically opposite the cranks 20.

The head ends of the two cylinders 15 and 16 are interconnected by atransfer conduit 25 through which the gas trapped above the pistons 22,which gas constitutcs the working medium of the Stirling engine, istransferred back and forth between the cylinders as the crankshaftrotates. As shown, the cylinder 15 constitutcs the hot space of theStirling engine, and it, together with the adjacent end of the conduit25, is provided with a jacket 26 connected through conduits 27 with theexhaust ports (not shown) of the cylinders 12 and 13. The jacket 26 hasan outlet opening communicating with an exhaust pipe 27.

The cylinder 16, which constitutcs the cold space of the Stirling engineshown, is provided With a coolant jacket 28, which desirably surroundsthe adjacent end of the conduit 25 as well as the cylinder 16. Thejacket 28 may be embodied in the same coolant circulating system as thatused to cool the first-stage cylinders 12 and 13; but if so, the jacket28 should desirably receive cold coolant directly from the radiator soas to maintain the cylinder 16 as cool as possible.

Ideally, a Stirling engine operates on a cycle in which the workingmedium is successively compressed isotherrr lly to minimum volume,heated at the minimum volufne, permitted to expand isothermally tomaximum volume while doing work, and then cooled at the maximum volume.In an actual engine, there is more or less overlapping of successivesteps of the cycle, the extent of such overlapping depending on theparticular design of the engine. The Stirling engine shown by Way ofexample in the drawings, provides considerable overlapping of successivecycle-Steps, but it possesses several advantages which tend tocompensate for such loss in efficiency as results from the overlapping.As shown in FIG. 2, the crank 24 is at the lowermost point of its pathof travel, the working medium trapped above the pistons 22 has itsmaximum volume, and the engine has therefore just completed its Workingstroke. Compression of the working medium will occur as the crank 24moves from its lowermost position to its uppermost position, when theworking stroke and expansion of the working medium will begin. As willbe clear from FIG. 2, where the crankshaft is indicated as rotating in aclockwise direction, movement of the Crank 24 from its lowermostposition will be accompanied by outward movement (relative to thecrankshaft) of the piston in cylinder and inward movement of the pistonin cylinder 16, and a displacement of the working medium toward thecooled cylinder will therefore result. Such displacement will continuefor approximately onefourth of a revolution, or until the time when thepiston in cylinder 16 will have reversed its direction and acceleratedto an outward Velocity which equals and begins to exceed that of thedecelerating piston in cylinder 15. Thereafter, the displacement of theworking medium will be in the general direction of the heated space ofthe engine, and such displacement will continue for about one-half arevolution, when both pistons will be moving inwardly and the piston incylinder 16 attains an inward Velocity which equals and begins toexceeds that of the piston in cylinder 15, whereupon the displacement ofthe working medium will be reversed. It is thus apparent that in theStirling engine shown the working medium will be heated during the laststage of its compression and the first stage of its expansion and cooledduring the final stage of its expansion and the initial stage of itscompression.

The efficiency of a Stirling engine can be increased by providing aregenerator or heat sink in the passage through which the working mediumflows between the hot and cold spaces of the engine. Such a regenerator,indicated by the reference numeral 30, is shown in FIG. 2 in thetransfer conduit 25. The regenerator may be any means which possessesadequate thermal capacity and a relatively large surface area and whichoffers little obstruction to the flow of gas through the conduit 25. Amass of metal wool or a series of juxtaposed disks of fine- Wire meshconstitutes a suitable regenerator.

The specific power plant illustrated in the drawngs has severaladvantages, especially where the internal combustion engine is of thefour-stroke cycle type and has two cylinders. Locating the Stirlingengine, or at least the hot-space thereof, between two cylinders of theinternal combustion engine facilitates the ducting through which theexhaust from the internal-combustion engine is conducted to such hotspace. If, the two four-cycle cylinders 12 and 13 are arranged to firealternately, the power plant provides a substantially uniformdistribution of the torque impulses, the torque impulses of the Stirlingengine, which occur at one-revolution intervals, alternating with thetorque impulses of the two-cylinder internalcombustion engine, which incombination likewise occur at one-revolution intervals. Further, theexhaust strokes of the internal-combustion cylinders coincideapproximately with the intervals in which the working medium of theStirling engine is to be heated. The primary inertia forces of thereciprocating parts produce no substantial rocking couples and can beeffectively suppressed by the employment of appropriate counterweightson the crankshaft.

For known reasons, it is desirable that the gaseous working medium of aStirling engine be maintained under a substantial pressure, and tolessen the possibility of the escape of the working medium past thepistons, as well as for other reasons, it is desirable to maintan theinner faces of the pistons under fluid pressure comparable to theaverage pressure of the working medium. I have therefore shown (FIG. 3)the crankcase 10 as provided with spaced partitons 32 which are locatedon opposite sides of the crank 24 and which cooperate with the pistonsand the walls of the crankcase to define an enclosed space the gas nwhich may be maintained under appropriate pressure in any convenientmanner.

In an internal-combustion engine operating under varying speeds andloads, wide variations occur in the temperature of the exhaust gases;and when the exhaust gases are used to heat the hot space of a Stirlingengine, the output of the latter engine will vary with the temperatureof the exhaust gases. Low-temperature exhaust gases from an internalcombustion engine normally contain a substantial amount of unbumed fuelwhich, in accordance with my invention. I employ to raise thetemperature that otherwise would exist in the hot space of the Stirlingengine. One arrangement for accomplishing that purpose is indicateddiagrammatically in FIG. 4, where the exhaust gases from an internalcombustion engine are shown as being conducted to the hot-space jacket36 of a Stirling engine through a conduit having two branches 37 and 38.Flap valves 39 and 39' located at the junctions of the two branches 37and 38 are employed to open one branch and close the other. Such flapvalves may be operated automatically by means 40 responsive to thetemperature of the exhaust gases leaving the internal combustion engine35. When the temperature of the exhaust gases is relatively low, thevalves 39 and 39' are positoned as shown to direct flow through thebranch 38 which contains means for burning any unburned components inthe exhaust gases. As shown, the branch 38 has an opening 42 foradmitting the auxiliary air necessary to combustion and is also providedwith an igniter 43, which may be a simple glow plug. In addition to theauxiliary air opening and igniter, or as an alternative for the igniter,the branch 38 contains a mass 44 of an oxidation catalyst. Mostoxidation catalysts which have been used to promote the combustion ofunburned components in exhaust gases operate most effectively atrelatively high temperatures; and while such a Catalyst may eventuallyattain an effective temperature as a result of the combustion itinduces, the use of an igniter 43 to initiate combustion and promoterapid rise in the temperature-of the Catalyst 44 is usually desirable.

If the internal combustion engine 35 of FIG. 4 is operating underconditions which result in high exhaust-gas temperature andsubstantially complete fuel consumption, the temperature-responsivemeans 40 will swing the valves 39 and 39' to close the branch 38 andopen the branch 37, which provides free passage of the exhaust to thehotspace jacket 36 of the Stirling engine. By-passing of hightemperaturegases around the auxiliary air-opening 42 and the Catalyst 44 avoidstheir diluton and Cooling by air which would enter through the opening42.

FIGS. 5 and 6 illustrate a power plant embodying the invention andsuitable for incorporation of a single-cylinder two-stroke cycleinternal combustion engine. Such power plant comprises a crankcasesupporting in coplanar relationship an intemal combustion cylinder 51and the two cylinders 52 and 53 of a Stirling-cycle engine. Thecylinders 51 and 52 are provided respectively with coolant jackets 54and 54', while the cylinder 53 is provided with a jacket 55 to which theexhaust from the cylinder 51 is conveyed through the branched conduit37-38 of FIG. 4. The two Stirling-cycle cylinders are interconnected attheir head-ends by a transfer conduit The power plant shown in FIG. 5conveniently embodies a crankshaft 57 of the form shown diagrammaticallyin FIG. 6. Such crankshaft has cranks 58, 59, and connected respectivelythrough connecting rods to the pistons 61, 62, and 63 in the cylinders51, 52, and 53. The cranks are arranged at equal angular intervals aboutthe axis of the crankshaft 57, with the Crank 59 leading and the crank60 trailing the Crank 58 in rotation in the contemplated direction,which is the counterclockwise direction as indicated by the arrow inFIG. 6.

Like the crankcase 10 of FIGS. l-4, and for the same purpose, thecrankcase 50 of FIG. 5 may be divided intemally by partition means toprovide a pressurized chamber with which the inner ends of the cylinders52 and 53 communicate.

In the crankshaft position shown in FIG. 6, the piston 61 in thecylinder 51 has just completed its power stroke and the working mediumof the Stirling engine is at minimum volume. During the approximately 90of crankshaft rotation prior to attainment of the crankshaft positionindicated in FIG. 6, the working medium of the Stirling engine was beingdisplaced from the cold cylinder 52 to the hot cylinder 53, anddisplacement in that sense will Continue for approximately an additional90 of crankshaft rotation, whereupon the ow of the working medium willbe reversed and displacement from the hot cylinder to the cold cylinderwill occur. As the heated working medium begins to expand followingattainment of the crankshaft position shown in FIG. 6, it will performwork on the piston 63 with the result that a torque impulse will beimposed on the crank 60. During the working stroke of the piston 63 thepiston 61 will be compressing the charge in the cylinder 51.Charge-compression will be completed after 180 of crankshaft revolutionfrom the position shown in FIG. 6 at which time the working medium ofthe Stirling engine will have attained its maximum volume.

It will thus be obvious that in the power plant of FIGS. 5 and 6 therespective torque impulses of the two-stroke cycle internal combustionengine 51 and of the Stirling engine will be substantially equallyspaced. By suitable coordination of the throws of the cranks 58, 59, and60 and the masses of the pistons 61, 62, and 63, primary and secondaryinertia forces can be balanced.

It may be noted that in its broad aspect the invention of thisapplication is not limited to any particular form or type for theinternal combustion engine or the Stirling engine. The two arrangementsshown for purposes of illustrating the invention have certain advantagesis respect to simplicity of construction, economy of manufacture, anddynamic balance, as well as other advantages. The arrangements of thecylinders of a two-cylinder Stirling engine in a common plane, as inFIGS. 5 and 6, or perpendicularly to each other, as shown in FIGS. 1-3,may not be the Optimum arrangement from the standpoint ofStirling-engine efficiency; and if so, it would be possible to improvethe eficiency of the Stirling engine by altering the effective anglebetween its two cylinders. Any such improvement, however, would beobtained at the expense of complicatng the problem of balancng inertiaforces.

I claim as my invention:

1. A two-stage power plant comprising an internalcombustion engine as afirst stage and a Stirling-cycle engine as a second stage, said twoengines having a common crankshaft, said Stirling engine having meansproviding intercommunicating heated and cooled chambers and including acylinder and a piston reciprocable in the cylinder for confining a bodyof gaseous working medium, said internal-combustion engine including atleast one cylinder and a piston reciprocable therein, said crankshafthaving a separate crank for each of said cylinders, connecting rodsoperatively interconnecting said cranks respectively with said pistons,ducting for conveying exhaust gases from the intemal-combustion engineinto heat transferring relation to said heated chamber, and meanslocated in said ducting for burning unburned components of said exhaustgases.

2. A two stage power plant, comprising an internalcombustion engine as afirst stage and a Stirling-cycle engine as a second stage, saidintemal-combustion engine being of the four-stroke cycle type andincluding two coplanar cylinders, said Stirling-cycle engine having apair of cylinders disposed between the two intemal-combustion enginecylinders and arranged at an angle to each other generally symmetricallyrelative to the common plane of the intemal-combustion engine cylinders,a piston in each of said cylinders, a common crankshaft for the twoengines, said crankshaft having two coaxial end cranks connected byconnecting rods to the pistons in the internal-combustion enginecylinders and an intermediate Crank spaced substantially l from said endcranks and connected by connecting rods to the pistons in the cylindersof the Stirling-cycle engine, a transfer conduit nterconnecting the headends of the latter cylinders, a jacket for one of the cylinders of theStirling-cycle engine, ducting for conveying exhaust gases to saidjacket from the cylinders of the internal-combustion engine, meanslocated in said ducting for burning unburned components of said exhaustgases and means for cooling the other cylinder of the Stirling-cycleengine.

3. A two stage power plant, comprising an intemalcombustion engine as afirst stage and a Stirling-cycle engine as a second stage, saidStirling-cycle engine comprising two cylinders and a transfer conduitinterconnecting their head ends, pistons in said cylinders, saidinternalcombustion engine being of the two-stroke cycle type and havinga single cylinder containing a piston, all three of said cylinders beingat least approximately coplanar, a common crankshaft for said engines,said crankshaft having three cranks spaced at substantially equalangular intervals about the crankshaft axis and connected by connectingrods to the three pistons respectively, one of said Stirling-enginecylinders being provided with a jacket, ducting for conveying exhaustgases from the intemaloombustion engine to said jacket, and meanslocated in said ducting for burning unbumed components of said exhaustgases.

4. A power plant as set forth in claim 3 with the addition that saidinternal-combustion engine cylinder and said jacketed cylinder of theStirling-engine are located on opposite sdes of the otherStirling-engine cylinder.

References Cited by the Examiner UNITED STATES PATENTS 2,196,979 4/40Campbell 60-14 2,590,5l9 3/52 Du Pre 60-24 2,6l6,250 11/52 YZer 60-242,907,169 10/59 Newton 60-24 EDGAR W. GEOGHEGAN, Primary Examiner.

SAMUEL LEVINE, ROBERT R. BUNEVICH, I ULUS E. WEST, Examiners.

1. A TWO-STAGE POWER PLANT COMPRISING AN INTERNALCOMBUSTION ENGINE AS A FIRST STAGE AND A STIRLING-CYCLE ENGINE AS A SECOND STAGE, SAID TWO ENGINES HAVING A COMMON CRANKSHAFT, SAID STIRLING ENGINE HAVING MEANS PROVIDING INTERCOMMUNICATING HEATED AND COOLED CHAMBERS AND INCLUDING A CYLINDER AND A PISTON RECIPROCABLE IN THE CYLINDER FOR CONFINING A BODY OF GASEOUS WORKING MEDIUM, SAID INTERNAL-COMBUSTION ENGINE INCLUDING AT LEAST ONE CYLINDER AND A PISTON RECIPROCABLE THEREIN, SAID CRANKSHAFT HAVING A SEPARATE CRANK FOR EACH OF SAID CYLINDERS, CONNECTING RODS OPERATIVELY INTERCONNECTING SAID CRANKS RESPECTIVELY WITH SAID PISTONS, DUCTING FOR CONVEYING EXHAUST GASES FROM THE INTERNAL-COMBUSTION ENGINE INTO HEAT TRANSFERRING RELATION TO SAID HEATED CHAMBER, AND MEANS LOCATED IN SAID DUCTING FOR BURNING UNBURNED COMPONENTS OF SAID EXHAUST GASES. 